Machining parts in the deformation, is more difficult to solve the problem. First, we must analyze the causes of deformation, and then take measures to deal with.
First:the workpiece material and structure will affect the deformation of the workpiece.
The amount of deformation and shape complexity, aspect ratio and wall thickness is proportional to the rigidity and stability of the material is proportional to. Therefore, the design of parts as much as possible to reduce the impact of these factors on the deformation of the workpiece.
Especially in the structure of large parts should be more reasonable structure. In the processing of rough hardness before, loose and other defects strictly controlled to ensure the quality of the rough to reduce the deformation of the workpiece.
Second:the workpiece clamping caused by deformation
Workpiece clamping, we must first select the correct clamping point, and then select the appropriate clamping force clamping position. Therefore, as far as possible, the clamping point and the support point are the same, so that the clamping force acts on the support. The clamping point should be as close as possible to the processing surface, and the position where the clamping force is not easily selected should be chosen.
When there are several directions on the workpiece clamping force, to consider the order of the clamping force, the workpiece and the support for the contact clamping force should be the first role, and not easy too much, the main clamping force for the balance of cutting force , Should be used at the end.
Second, to increase the contact area of the workpiece and the fixture or the use of axial clamping force. Increasing the rigidity of the part is an effective solution to the problem of clamping deformation. However, due to the shape and structure of the thin-walled part, it has lower rigidity. This clamping force in the role, it will have deformation.
Increase the contact area of the workpiece and the fixture, which can effectively reduce the deformation of the workpiece when clamping. Such as milling thin-walled parts, the extensive use of elastic plate, the purpose is to increase the contact parts of the force area; in the thin-walled inner diameter and outer circle, whether it is a simple open transition ring, or the use of elastic mandrel , The whole arc claw, etc., are used to increase the contact area when the workpiece clamping. This method is conducive to carrying clamping force, in order to avoid the deformation of the parts. The use of axial clamping force, is also widely used in the production, design and production of special fixture can make the clamping force on the end, you can solve the workpiece wall thin, poor rigidity, resulting in bending deformation of the workpiece.
Third:the workpiece deformation caused by processing
Workpiece in the cutting process due to the role of cutting force, resulting in the direction of the force to the elastic deformation, that is, we often say that the knife phenomenon. To deal with such deformation in the tool to take appropriate measures, finishing requires sharp tool, on the one hand can reduce the friction between the tool and the workpiece formed by the resistance, on the other hand can improve the cutting tool cutting heat dissipation capacity, thereby reducing the workpiece Residual internal stress. For example, in the milling of thin-walled parts of the large plane, the use of single-edged milling method, the tool parameters selected a larger primary angle and a larger rake angle, the purpose is to reduce cutting resistance. Because of this cutter cutting light, reducing the deformation of thin-walled parts, in the production has been widely used. In the thin-walled parts of the turning, a reasonable tool angle cutting the size of turning force, turning the heat generated by the deformation, the micro-quality of the workpiece surface are crucial. The size of the rake angle determines the sharpness of cutting deformation and tool rake angle. Large anterior horn, cutting deformation and friction decreases, but the anterior horn is too large, will reduce the wedge angle of the tool, the tool weakened, poor cooling tool, wear and tear accelerated. Therefore, the general turning steel parts thin-walled parts, the use of high-speed tool, the front angle 6 ° ~ 30 °, with carbide cutting tools, the front angle to take 5 ° ~ 20 °. Large tool clearance, friction, cutting force is also reduced, but too large after the corner will make the tool weakened. In the thin-walled parts, the use of high-speed steel turning tool, the tool after the angle to take 6 ° ~ 12 °, with carbide tools, after the angle to take 4 ° ~ 12 °, fine car take a larger relief angle, rough car Take a smaller clearance angle. When thin-walled car parts inside and outside the circle, take a large main angle. Correct selection of tools is necessary to deal with the deformation of the workpiece.
During processing, the heat generated by the friction between the tool and the workpiece can also deform the workpiece, so in many cases, high-speed cutting is selected. In high-speed machining, the cutting chips are cut off in a relatively short period of time, most of the cutting heat is taken away by the chips, reducing the thermal deformation of the workpiece. Secondly, in high-speed machining, due to the reduction of the softened portion of the cutting layer material Can reduce the deformation of parts processing, is conducive to ensuring the size of parts, shape accuracy. In addition, the cutting fluid is mainly used to reduce the friction during cutting and reduce the cutting temperature. Rational use of cutting fluid to improve the durability of the tool and the processing surface quality, processing accuracy has an important role. Therefore, in the processing of parts in order to prevent deformation must be reasonable use of adequate cutting fluid.
The use of a reasonable amount of cutting processing is the key factor to ensure the accuracy of parts. In the processing of high precision thin-walled parts, the general take symmetrical processing, so that the relative stress generated on both sides of the balance, to a steady state, after the formation of the workpiece. However, when a certain process to take a larger amount of knife, due to tensile stress, compressive stress out of balance, the workpiece will have deformation.
Thin-walled parts turning deformation is multi-faceted clamping force when clamping the workpiece, the cutting force when cutting the workpiece, the workpiece hinders the cutter cutting elastic deformation and plastic deformation, the cutting zone temperature rise and thermal deformation. Therefore, we have to rough the back, eat the amount of knife and feed can take larger; finishing, the amount of knife is generally 0.2 ~ 0.5mm, the feed is generally 0.1 ~ 0.2mm / r, or even smaller , Cutting speed of 6 ~ 120m / min, finishing with high cutting speed, but not too high. Reasonable choice of cutting dosage, so as to achieve the purpose of reducing the deformation of parts.
Fourth:the stress after processing deformation
After processing, there is inherent stress in the parts. The internal stress distribution is a relatively balanced condition. The shape of the parts is relatively stable. However, after some materials are removed and the internal stress changes after the heat treatment, the work piece needs to regain the balance of forces. Has changed. Solve such deformation can be heat treatment methods, the need to straighten the workpiece stacked into a certain height, with a certain tooling pressed into a flat state, and then the tooling and the workpiece into the furnace, according to the different parts of the material, choose Different heating temperature and heating time. Hot straightening, the internal organization of the workpiece stable. At this point, the workpiece has not only been a high degree of straightness, but also to eliminate work hardening phenomenon, easier to further refine the parts. Casting to be aging treatment, try to eliminate the internal residual stress, the use of deformation and then processing methods, namely roughing - aging - re-processing.
For large parts to be profiling, which is expected after the deformation of the workpiece assembly, processing in the opposite direction to set aside the amount of deformation, which can effectively prevent the deformation of the assembly after assembly.
In summary, for the easy deformation of the workpiece, the blank and the processing technology must adopt the appropriate countermeasures, according to different circumstances to be analyzed, will find a suitable process route. Of course, the above method is only to further reduce the deformation of the workpiece, if you want to get a higher precision workpiece, you still need continuous learning, research and research.
